The present invention relates to an ink jet recording apparatus in which a linear array of small nozzles and pressure generators communicating with respective ones of those nozzles are provided, and dots are formed on a recording sheet in such a manner that the pressure generators pressure feed ink to the nozzles, and in turn the nozzles shoot ink jets onto the recording sheet. More particularly, the present invention relates to a technique for removing light printing defects due to paper particles, dust, and like, and heavy printing defects due to mixing of air bubbles into the ink jets.
In an ink jet recording apparatus, a linear array of small nozzles, each about 100 .mu.m in diameter, is formed on the top of the print head. To effect printing with this apparatus, the print head is moved over the surface of a recording sheet by a carriage. However, during the printing process, paper particles from the recording sheet and dust stuck to the same tend to adhere to the nozzle openings. The nozzles thus tend to get clogged with the paper particles and dust. This leads to printing defect. Also, air bubble sometimes enter into a connecting portion between the ink tank and the nozzles. In an extreme case, the supply of ink to the nozzles is halted, resulting in no print.
To cope with the problems mentioned above, an ink sucking device in which a negative pressure generating unit, which applies a negative pressure to a cap member for hermetically sealing the nozzle openings of the print head, is installed in the printer. When a printing defect occurs, the user pushes a print recovery button on a control panel. Then, the negative pressure generating unit is driven to produce a negative pressure within the space of the cap member, and hence to forcibly expel a larger amount of ink from the nozzles than in normal printing. With the sucking of the ink, paper particles and dust adhering to the nozzle openings are washed away with the ink jets. In this way, the printer is recovered from the clogging of the nozzles.
Air bubbles are normally present outside from the nozzle openings. The ink thus must be sucked up in such an amount as to extract the air bubble from the nozzle openings. Accordingly, to eliminate air bubbles, the amount of the sucked ink is much larger than that for removing paper particles and dust.
Thus, the forcible discharge of the ink consumes a great amount of ink, which is much larger than that in normal printing. To avoid idle consumption of excessive amounts of ink during maintenance, the usual practice is to limit the amount of ink discharged for each operation of the recovery switch to a preset value. The amount of ink discharged during one suction operation is set at such an amount as to remove the clogging of the nozzles that frequently occurs due to accumulation of paper particles and dust thereon. This amount is 0.5 cc, for example. Therefore, if a user mistakenly pushes the recovery button, the amount of ink consumed is about 0.55 cc at most.
In case where about 2 cc of ink must be discharged, for example, to remove air bubble is removed, the recovery button must be pushed many times. This work is cumbersome for the user. The number of button pushings can be reduced by increasing the amount of ink discharged by one suction operation to such an extent as to remove the bubbles. Where the technique is employed, the ink is excessively discharged or sucked for curing light printing defects caused by paper particles and dust stuck to the nozzles, which frequently occurs.